0.5 V inverter‐based ultra‐low‐power, low‐noise VGA for medical ultrasound probes

Abstract

An inverter-based ultra-low-power, low-noise, single-ended to differential continuous-time variable gain amplifier is presented for 2-6 MHz second harmonic cardiac imaging ultrasound probes in a 65 nm CMOS technology. The proposed variable gain amplifier (VGA) consists of three equal inverters and resistor arrays which form a feedback loop. To improve both the power and noise performances, the inverters operate in the sub-threshold region by adopting a 0.5 V supply voltage. By doubling the input transconductance of the VGA, the noise figure (NF) is enhanced further. The 6-b thermometer resistor arrays achieve a gain range of the VGA from 0 to 22 dB. The total power consumption is 55 μW, NF is 2.7 dB referred to an 8 kΩ source resistor at a centre frequency of 4 MHz. 8-b thermometer calibration codes are added into the inverters to force the static operating point of the inverters to half of the supply voltage, which could increase the immunity of the second harmonic distortion (HD2) to the process variation. The HD2 of the proposed VGA is −60.6 dB at the 330 mV peak-to-peak output swing. The active size is 154 × 102 μm.

Inverter-based low-noise, 150 µW single-ended to differential SC-VGAs for second harmonic cardiac ultrasound imaging probes

“…Hence, the inverter-based SC-VGA is sensitive to the process variation. To reduce the influence of the process variation, calibration codes can be added to bring the bias point of the inverter back to V DD /2 as reported in [19]. In this work, the process variation is not considered.…”

A 0.74 mW, linear-in-dB, constant bandwidth, variable gain amplifier based on zero-pole repositioning technique

“…It is mostly used in automatic gain control (AGC) loops to automatically adjust the gain of received signal. Beside the vast application in wireless communication systems, VGAs are also widely used in many other applications such as disk drivers, wireless sensor networks (WSN), and medical applications especially in medical ultrasound imaging [2][3][4][5][6][7][8].…”